Method and apparatus for automatic sizing and positioning of ABS sampling window in an x-ray imaging system

Abstract

A method for providing automatic brightness control in a closed loop x-ray imaging system which utilizes an automatic brightness system (ABS) sampling window. The location, size and shape of the ABS sampling window is adjusted in accordance with statistical information including spatial gray scale distribution data derived from the data related to the x-ray system and image being processed, thereby enabling the automatic brightness control to make brightness and power adjustments in accordance with statistical data from the modified ABS sampling window.

What is claimed is:  
     
       1. A method for determining the size, position and shape of an automatic brightness system (ABS) sampling window in an x-ray image and adjusting brightness of the image in a closed loop x-ray imaging system, said method comprising the steps of: 
       (a) determining size of the ABS sampling window, based on a function of a generator kVp value;  
       (b) determining position of the ABS sampling window based on a spatial gray scale distribution within an image region of interest;  
       (c) determining geometry of the ABS sampling window based on collimation of x-rays in the system; and  
       (d) adjusting a brightness control of the image in accordance with data obtained from the ABS sampling window as modified in steps (a)-(c), to thereby compensate for the deleterious effects of improper patient positioning, variations in patient size, and rapid changes from torso to extremity imaging.  
     
     
       2. The method as in claim  1  wherein the step of determining the size of the automatic brightness system (ABS) sampling window further comprises the steps of: 
       finding a diameter for the ABS sampling window in centimeters using a kilovolt potential value from a high voltage generator;  
       dividing the diameter by the image intensifier mode in centimeters to derive an ABS sampling window percentage in relation to a full image diameter; and  
       setting the ABS sampling window diameter to the ABS sampling window percentage of the full image diameter.  
     
     
       3. The method as in claim  2  wherein the step of finding a diameter for the automatic brightness system (ABS) sampling window in centimeters using a kilovolt potential value from a high voltage generator further comprises, subtracting 40 from the kilovolt potential value and dividing the value by two. 
     
     
       4. The method as in claim  1  wherein the step of determining size of the automatic brightness system (ABS) sampling window based on a function of a generator kVp value further comprises, determining size of the ABS sampling window based on a function of a generator kVp and an image receptor mode. 
     
     
       5. The method as in claim  1  wherein the step of determining the size of the automatic brightness system (ABS) sampling window further comprises determining an intensifier mode based on an image intensifier size, and an image intensifier magnification mode. 
     
     
       6. The method as in claim  1  wherein the step of determining the size of the automatic brightness system (ABS) sampling window further comprises selecting an ABS sampling window size which constrains the maximum and minimum size of a full image viewing diameter. 
     
     
       7. The method as in claim  6  wherein the automatic brightness system (ABS) sampling window is constrained to be between 40 to 70 percent of the full image viewing diameter. 
     
     
       8. The method of claim  1  where the step of determining the shape of the automatic brightness system (ABS) sampling window based on the collimation of x-rays in the system further comprises modifying the sampling window to account for the encroachment of collimators into the ABS sampling window. 
     
     
       9. The method of claim  1  wherein the step of determining the position of the automatic brightness system (ABS) sampling window, further comprises the steps of: 
       (1) selecting a region of interest within the image being processed;  
       (2) dividing the region of interest into a plurality of segments; and  
       (3) determining an ABS sampling window position based on gray scale distribution within the image by comparing the proportional gray scale values of the segments.  
     
     
       10. The method as defined in claim  9  wherein the step of selecting a region of interest within the image displayed further comprises the step of generating a circular blanking area within the image, wherein the region of interest is selected from within the circular blanking area. 
     
     
       11. The method as defined in claim  9  wherein the step of selecting a region of interest within the image further comprises the step of establishing an automatic brightness system (ABS) sampling window within the region of interest, wherein statistical gray scale distribution data within the ABS sampling window is utilized to determine proper adjustments to be made to the brightness of the image. 
     
     
       12. The method as defined in claim  9  wherein the step of dividing the region of interest into a plurality of segments further comprises the step of selecting the automatic brightness system (ABS) sampling window to encompass a circular region of the image. 
     
     
       13. The method as defined in claim  12  wherein the step of dividing the image region of interest (ROI) sampling window into quadrants further comprises the step of dividing the image region of interest (ROI) into equally sized quadrants. 
     
     
       14. The method as defined in claim  9  wherein the step of determining an ABS sampling window position based on gray scale distribution within the image by comparing the proportional gray scale values of the segments further comprises the step of moving the automatic brightness system (ABS) sampling window such that measurements of statistical data within the ABS sampling window will enable the system to make adjustments to the brightness control system to obtain an improved image on the monitor. 
     
     
       15. The method as defined in claim  14  wherein the step of moving the automatic brightness system (ABS) sampling window further comprises the step of first determining an X offset value and a Y offset value for the ABS sampling window. 
     
     
       16. The method as defined in claim  15  wherein the step of determining an X offset value and a Y offset value for the automatic brightness system (ABS) sampling window further comprises the steps of: 
       (1) determining an average gray scale value for each of the segments of the image region of interest (ROI); and  
       (2) determining the X offset value and the Y offset value utilizing the average gray scale values of each of the segments, and the size of the region of interest.  
     
     
       17. The method as defined in claim  16  wherein the step of determining the average gray scale value for each of the segments of the image region of interest (ROI) sampling window further comprises the step of executing the following equation for each of the segments: 
       
         
             Q ( n )% GS=Q ( n )Average GS /SumOf Q Averages  
         
       
       where: 
       Q(n)%GS=the percentage of gray scale distribution within a segment n,  
       Q(n)AverageGS=the average gray scale distribution in a segment n,  
       SumOfQAverages=the sum of the average gray scale distribution in all the segments 1 through n.  
     
     
       18. The method as defined in claim  16  wherein the step of determining the X offset value and the Y offset value utilizing the average gray scale values of each of the four segments further comprises the step of determining the X offset value utilizing the following equation: 
       
         
             X off=( ROI Size/2)−( ROI Size×( Q 2% GS+Q 4% GS ))  
         
       
       where: 
       Xoff=the X offset value of the automatic brightness system sampling window,  
       ROISize=the total number of pixels across the X axis of the region of interest,  
       Q2%GS=the percentage of gray scale distribution within a second segment,  
       Q4%GS=the percentage of gray scale distribution within a fourth segment.  
     
     
       19. The method as defined in claim  16  wherein the step of determining the X offset value and the Y offset value utilizing the average gray scale values of each of the four segments further comprises the step of determining the Y offset value utilizing the following equation: 
       
         
             Y off=( ROI Size2)−( ROI Size*( Q 3% GS+Q 4% GS )  
         
       
       where: 
       Yoff=the Y offset value to be applied to the automatic brightness system sampling window,  
       ROISize=the total number of pixels across Y axis of the region of interest  
       Q3%GS=the percentage of gray scale distribution within a third, segment,  
       Q4%GS=the percentage of gray scale distribution within a fourth segment.  
     
     
       20. The method as defined in claim  16  wherein the method further comprises the step of using a ratio of an average gray scale distribution of the entire automatic brightness system image region of interest (ROI) versus a segment gray scale to thereby adjust the positioning of the ABS sampling window, in accordance with a thickness of a patient's anatomy being x-rayed and displayed on the monitor. 
     
     
       21. The method as defined in claim  15  wherein the method further comprises the step of dampening movement of the automatic brightness system (ABS) sampling window by utilizing temporal averaging. 
     
     
       22. The method as defined in claim  9  wherein the step of determining an ABS sampling window position based on gray scale distribution within the image by comparing the proportional gray scale values of the segments further comprises the step of establishing an upper threshold and a lower threshold for ignoring gray scale values to thereby avoid skewing gray scale distribution values. 
     
     
       23. The method as defined in claim  22  wherein the method further comprises the step of eliminating a portion of the image region of interest (ROI) sampling window from calculations for determining spatial gray scale distribution if part of an x-ray exposure is outside said upper and lower thresholds. 
     
     
       24. The method as defined in claim  9  wherein the step of dividing the image region of interest (ROI) sampling window into a plurality segments further comprises the steps of centering the segments about an origin of the image Region of interest (ROI) sampling window, such that the plurality of segments are not in contact with each other, and are equally spaced about the origin. 
     
     
       25. A method for making automatic adjustments to brightness of an image displayed on a monitor in a closed loop x-ray imaging system, said method comprising the steps of: 
       (1) selecting a region of interest within the image;  
       (2) establishing an automatic brightness system (ABS) sampling window within the region of interest;  
       (3) adjusting a position of the ABS sampling window through measurements of statistical gray scale distribution within the ABS sampling window; and  
       (4) adjusting the brightness of the image in accordance with the gray scale statistics within the ABS sampling window, to thereby compensate for the deleterious effects of improper patient positioning, variations in patient size, and rapid changes from torso to extremity imaging.  
     
     
       26. The method as in claim  25  where in step of adjusting a position of the automatic brightness system (ABS) sampling window further comprises the step of adjusting the position of the automatic brightness (ABS) window based on a spatial gray scale distribution in a segment as compared against at least one other segment which has a spatial gray scale distribution within an image region of interest (ROI). 
     
     
       27. Apparatus for determining the size, position and shape of an automatic brightness system (ABS) sampling window in an x-ray image and making adjustments to brightness of the image in a closed loop x-ray imaging system in response to gray scale data in the adjusted ABS sampling window, comprising: 
       a position processor coupled to the x-ray imaging system to position the ABS sampling window in the x-ray image received from the x-ray imaging system, based on a spatial gray scale distribution wherein said selected segment has a desirable statistical gray scale distribution within the region of interest;  
       a size processor coupled to the position processor, to determine the size of the ABS sampling window based on a function of a generator kVp value;  
       a shape processor coupled to the sizing processor, to determine the shape of the ABS sampling window based on x-ray collimation in the x-ray imaging system;  
       a statistical processor coupled to the shape processor to receive the ABS sampling window data and to generate statistical information based on ABS sampling window data; and  
       an automatic brightness control coupled to the statistical processor to adjust brightness of the image in accordance with statistical information obtained from the statistical processor regarding the modified ABS sampling window to thereby compensate for the deleterious effects of improper patient positioning, variations in patient size, and rapid changes from torso to extremity imaging.